For most applications, it is widely recognised that encoders provide the best solution for motion feedback. Whilst there are a few different types of encoder available on the market, optical encoders generally deliver the highest accuracy and resolution. However, because they are optical, they can be subjected to various forms of contamination and can suffer from shock and vibration conditions. For such harsh conditions they are not considered as suitable as either magnetic or inductive encoders.
There are two types of optical encoders, the incremental and the absolute. Both are available in either linear or rotary form.
Motion Control Products offer a range of optical encoders (both incremental and absolute encoders) that provide position information for a rotating shaft by producing a continuous series of pulses. Our encoders can be supplied with a concise range of options from through hole to shaft encoders, in a range of diameters and options.
The range includes the encoder modules kits with outside diameters from 20mm, 28mm to 40mm, the encoders with a range of bore holes and complete hollow shaft, and the shaft encoders from 35mm up 50mm in diameter with a host of resolutions and electrical specifications.
Incremental Encoder Features
Incremental Encoders generate electrical signals by means of a rotating disk that passes between a light source and photo detectors. This type of encoder has two output signals, (or channels), most commonly referred to as channels A and B. The two channels, A and B, are commonly 90 electrical degrees out of phase and the electronic components determine the direction through recognition of the phase relationship between the two channels. The position of an incremental encoder is done by adding up all the pulses by a counter. One drawback of the incremental encoder is the count loss which occurs during power loss. When restarting, the equipment must be referenced to a home position to reinitialize the counter. Incremental encoders often provide a third output that pulses once per revolution of the disk. This is typically called the Index, or Z-channel, and is commonly used for homing/reference moves.
Absolute Encoder Features
An absolute encoder contains components also found in incremental encoders. They implement a photo-detector and LED light source but instead of a disk with evenly spaced lines on a disc, an absolute encoder uses a disk with concentric circle patterns. Absolute encoders have a unique value (voltage, binary count, etc.) for each mechanical position. When an absolute encoder is powered on, the position is known. Absolute encoders most commonly provide digital data in a parallel or serial format to the motion controller which is used to determine position/velocity information. Since they provide absolute position information when powered on, they eliminate the need for a homing/reference move in a motion system.
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